const jokeEl = document.getElementById('joke');
const jokeBtn = document.getElementById('joke-btn');

const generateJoke = () => {

const xhr = new XMLHttpRequest();
   xhr.open('GET', 'https://api.chucknorris.io/jokes/random',true);
   xhr.onreadystatechange = function () {
   if (this.readyState === 4) {
     if (this.status === 200) {
    const joke = JSON.parse(this.responseText).value;
    jokeEl.innerHTML = joke;
} else {
    jokeEl.innerHTML = '出现错误，不好笑。';
    }
    }
   };
   xhr.send();
}
jokeBtn.addEventListener('click',generateJoke);
document.addEventListener('DOMContentLoaded',generateJoke);